Coated metal container



9, 1966 L. R. KOHAN ETAL 3,265,239

COATED METAL CONTAINER Original Filed Oct. 25, 1962 I NVENTORS. Lf0/1/4190 2/! YMflA/D KO/v A N JOHN ANTHONY STOP 1 65 United StatesPatent 6 Claims. (Cl. 220-6 1) This application is a division of myco-pending application, Serial No. 232,559, filed October 23, 1962, nowPatent No. 3,180,928.

This invention relates to a coated seamless aluminum container and moreparticularly to an aluminum container having a form of aluminum oxidecoating on the surface thereof.

Many devices and processes are presently being used for forming seamlessaluminum containers from flat blanks. One of these procedures involvesfirst drawing the blank into a cup form by forcing the blank through adrawing die by means of a punch mounted upon a press. After drawing, thecup is passed through an ironing die, whose inside diameter is slightlysmaller than the outside diameter of the cup.

As drawn, the cup usually has bottom and sidewall thicknessessubstantially equal to the thickness of the blank. Ironing thins thesidewall of the drawn cup and forces the metal back, thereby alsoincreasing the height of the container. A plurality of ironing steps maybe performed to achieve a desired body wall thickness and containerheight.

Prior to the advent of these seamless containers, both interior andexterior decoration of metal cans, e.g., tin cans, had usually been doneupon the flat sheet prior to forming the cylinder. This was especiallytrue of the outside coating. However, with containers produced by thedrawing and ironing method, coatings were applied to the surface of thecontainer subsequent to its formation.

This necessitated the use of complex equipment to insure proper coverageand also precise registration when designs or lettering were utilized todecorate the container.

In addition, aluminum, which is used for many of these seamlesscontainers, often requires a primer coat for adherence of subsequentorganic coating. Even then, on occasion, considerable deterioration ofadhesion between the coating and the aluminum occurs on the interior ofthe containers used to package certain products, especially potableliquids. This results in corrosive attack upon the inner sidewall by theproduct and eventual spoilage of the contents of the container.

It is well known that aluminum is frequently anodized in order to forman aluminum oxide on the surface, which promotes organic coatingadhesion and resistance to corrosion. This oxide coating may also becolored for aesthetic purposes. The aluminum oxide formed in theanodizing process is generally porous and has a lower density thanconventional A1 0 which is used as an abrasive. This porous oxide maysubsequently be sealed by means of hydration in boiling water.

It is therefore an object of the present invention to provide athin-walled aluminum cup-shaped container having a coating of aluminumoxide thereon.

Another object is to provide an aluminum container which may bedecorated prior to forming.

A further object is to provide an oxide coated aluminum container whichis more readily receptive to an adherent organic coating.

Numerous other objects and advantages of the invention will be apparentas it is better understood from the following description, which, takenin connection with the accompanying drawings, discloses a preferredembodiment thereof.

The above objects are accomplished by providing a drawn and ironedone-piece aluminum container whose end has an as-anodized aluminumcoating thereon and whose sidewall is thinner than the thickness of theend. A discontinuous anodically formed aluminum oxide coating covers atleast one surface of the sidewall and the oxide coating comprises aplurality of discontinuous microscopic particles of aluminum oxideadhering to the aluminum basis metal, although the aluminum oxidecoating appears continuous to the naked eye.

Referring to the drawings:

FIGURE 1 is a fragmentary, enlarged, cross-sectional view of an anodizedaluminum sheet;

FIG. 2 is a perspective view of a coated container with parts brokenaway and partly in section; and

FIG. 3 is a photomicrograph of the exterior sidewall of the containerformed by drawing and ironing.

As a preferred or exemplary embodiment of the instant invention, a sheetof aluminum alloy 3003H-O is chemically anodized according to procedureswell known to those skilled in the art. If desired, it may also be colordyed by conventional procedures. FIGURE 1 shows a cross-section of thealuminum 6 with the anodic aluminum oxide 7 covering its surface.

A circular blank is cut from the coated aluminum and is formed into acontainer according to the method described in my copending applicationSerial No. 232,559, filed October 23, 1962, or by other suitable means.

As shown in FIG. 2, the drawing and ironing process produces acontainer, generally designated 12, having an integral end 14 and aseamless sidewall 16. The thickness of the end 14 is greater than thesidewall 16. For example, the end 14 may be 0.023 inch thick and thesidewall 16 may be 0.008 inch thick. This variation in thickness willdepend greatly upon the height and diameter of the container.

The bottom end 14 of the container 12 retains essentially the originalstructure of the as-anodized aluminum sheet and thus comprises thealuminum basis metal 6 coated with the anodized aluminum oxide 7.

On the other hand, the aluminum oxide coatings on the interior andexterior wall surfaces of the container 12 have been subjected tosubstantial mechanical deformation during the drawing and ironingoperation. The internal sidewall surface has been forced to undergo atensional bend during the drawing phase and a tensional force duringironing, whereas the exterior sidewall surface underwent a 90compressive bend in the drawing and was then exposed-to an extrusion orsqueezing action when being ironed.

As was noted hereinbefore, the bottom end 14 of the container 12 wasessentially undeformed during the drawing and ironing operation. Duringironing the sidewall 16 had been thinned substantially and elongated.Thus the sidewall 16 is thinner than the bottom end 14, although beingintegral therewith.

Since the aluminum oxide coating 7 produced by anodizing aluminum metal6 is generally considered to be quite brittle and barely amenable toeven slight bending, without fracturing, it is quite unexpected thatthis coating 7 could withstand extreme bending or an extrusion typedeformation such as is encountered in drawing and ironing, withoutexfoliating from the aluminum metal 6. Although the deformed oxide 7a onthe aluminum metal sidewall 16 does indeed remain adherent during thedrawing and ironing process, it nevertheless does not form a continuous,intact coating as found in undeformed anodized aluminum. However, theanodic coating 7 on the bottom end 14 of the container 12, which has notundergone deformation, remains essentially intact in the as-anodizedcondition.

Although the oxide coated surface of the exterior sidewall 16 appears asa shiny continous coating, metallographic examination reveals that thealuminum oxide 7a has been fractured during drawing and ironing andmicroscopic particles of aluminum oxide appear as islands adhering tothe aluminum basis metal. FIG. 3 shows the darker dyed oxide formation7a in relation to the exposed lighter aluminum 6. Even though the dullsurface appearance of the anodized metal has been converted to a shinysurface, somewhat lighter in shade than the asanodized and dyed color,the oxide is microscopically rough and discontinuous. This ironedsurface not only resists fingerprinting, which is a serious problem inhandling uncoated aluminum, but in addition exhibits a remarkableresistance to atmospheric corrosion.

On the other hand, the oxide coating 7b on the interior sidewall of thecontainer has not been ironed and therefore does not exhibit the brightsurface characteristic of an ironed anodically coated aluminum. Asmentioned hereinbefore, the interior side wall coating 7b has only beenforced to undergo a 90 tensional bend in the drawing operation and thenelongation during ironing. However, its microscopic appearance is quitesimilar to the exterior surface oxide 7a of the container 12. It isprobable that the separation of the oxide 7b on the interior sidewall isdue to metal stretching rather than extrusion or squeezing" as in theexterior sidewall.

It should be noted, however, that both the interior and exteriorsurfaces of the bottom end 14 of the container 12, which has neitherbeen drawn nor ironed, retain the as-anodized aluminum oxide coating,without the fractures found in the anodic coatings 7a, 7b on thesidewall 16 of the container 12.

Even though the interior oxide coating 7b on the container sidewall 16is not intact, it has been found that this surface provides moreadherent bonding for the subsequent application of organic coatings thana plain aluminum surface. This is especially true when the container isused for holding an alcoholic potable liquid.

It is thought that the invention and many of its attendant advantageswill be understood from the foregoing description and it will beapparent that the various changes may be made in the form, construction,and arrangement of the parts without departing from the spirit and scopeof the invention or sacrificing all of its material advantages, the formhereinbefore described being merely a preferred embodiment thereof.

We claim:

1. A drawn and ironed one-piece aluminum container,

comprising:

an end having an anodized aluminum oxide coating thereon;

a seamless sidewall, said sidewall having a thickness substantiallythinner than said end;

and a discontinuous anodic aluminum oxide coating covering at least onesurface of said sidewall, said oxide coating comprising a plurality ofdiscontinuous microscopic particles adhering to the aluminum basismetal, although said aluminum oxide coating appears continuous to thenaked eye.

2. The container of claim 1 wherein two surfaces of said sidewall arecoated with aluminum oxide.

3. The container of claim 1 wherein said aluminum oxide is dyed.

4. An aluminum container, comprising:

an end having a continuous anodized aluminum oxide coating thereon;

a seamless body whose sidewall is integral with said end, said sidewallhaving a thickness substantially less than the thickness of said end;

and a discontinuous aluminum oxide coating on at least one surface ofsaid sidewall, said oxide coating comprising a plurality ofdiscontinuous microscopic oxide particles adhered to the aluminum basismetal.

5. The container of claim 4 wherein the thickness of said end is greaterthan twice the thickness of said body sidewall.

6. A cup-shaped aluminum article of manufacture,

comprising:

a bottom coated with an adherent continuous chemically anodized aluminumoxide coating;

and an integral side coated with an adherent microscopicallydiscontinuous mechanically deformed aluminum oxide coating appearingcontinuous to the naked eye.

References Cited by the Examiner UNITED STATES PATENTS 3,031,387 4/1962Deal et al. 20438 3,061,447 10/1962 Brenner et al. 22064 3,120,3212/1964 McCuskey et al. 22064 THERON E. CONDON, Primary Examiner.

G. T. HALL, Assistant Examiner.

1. A DRAWN AND IRONED ONE-PIECE ALUMIUM CONTAINER, COMPRISING: AN END HAVING AN ANODIZED ALUMINUM, OXIDE COATING THEREON; A SEAMLESS SIDEWALL, SAID SIDEWALL HAVING A THICKNESS SUBSTANTIALLY THINNER THAN SAID END; AND A DICONTINUOUS ANODIC ALUMINUM OXIDE COATING COVERING AT LEAST ONE SURFACE OF SAID SIDEWALL, SAID OXIDE COATING COMPRISING A PLURALITY OF DISCONTINUOUS MICROSCOPIC PARTICLES ADHERING TO THE ALUMINUM BASIS METAL, ALTHOUGH SAID ALUMINUM OXIDE COATING APPEARS CONTINUOUS TO THE NAKED EYE. 